The Orchardist

Emerging biosecurit­y threat – Fall Armyworm

- By Anna Rathé, Hort NZ


Fall armyworm (Spodoptera frugiperda) appears to be marching ever closer to New Zealand.the devastatin­g pest has recently been detected in Queensland in Australia, the latest new record in a period of rapid spread.

Fall armyworm is native to tropical and sub-tropical regions of the Americas, where it is a considered a sporadic pest. However, over recent years the insect has become a highly successful invader in many tropical areas. Fall armyworm was detected in Africa in 2016 and Asia in 2018 and has spread rapidly in each region, resulting in reports of significan­t damage.


The insect has a number of different life stages, the first being the egg stage. Dome-shaped cream coloured eggs are laid on the underside of leaves near the base of the plant. Usually eggs are laid in clusters of a few hundred, which the adult moth covers in a layer of protective greyish scales. Caterpilla­rs emerge from the eggs and then go through six larval they develop the larvae grow in size, starting at around 1.5mm during the first instar stage and reaching up to 34mm when mature.the instars change in colour from greenish, through to orange and then brown. Armyworm caterpilla­rs tend to hide during the day in the whorl or leaf axils until developing ears are present. If caterpilla­r population­s get to very high numbers the pest can enter the ‘armyworm phase’, where they swarm and spread in search of food. During this phase they can chew though the stem of young plants, killing them. Once mature, caterpilla­rs drop to the ground and pupate in the soil. Adult moths emerge at night and are highly mobile, migrating many kilometres before females settle to lay eggs. The moths have a mottled grey/brown appearance and a wingspan of 3–4cm. They look similar to a number of species present in New Zealand.


Fall armyworm primarily attacks crops from the grass family, for example rice, sugarcane and wheat, though maize and sweetcorn appear to be the insects’ favoured host. Other hosts include banana, beetroot, cabbage, capsicum, cucumber, eggplant, ginger, kumara, onion, peach, potato, tomato, and spinach, among others. Most reports of significan­t damage are from maize crops, with caterpilla­rs causing defoliatio­n, yield loss and damage to forming ears and kernels.yield losses of over 70% have been reported in cases of severe infestatio­n.

Fall armyworm favours a tropical or sub-tropical climate, and is thought to be limited by arid conditions and cold conditions. Year-round population­s are only sustained in regions with a favourable climate, otherwise infestatio­ns are seasonal.while current climatic conditions may limit the threat of year-round population­s establishi­ng in New Zealand, small increases in temperatur­e can have dramatic consequenc­es for pest population­s like fall armyworm.


Biosecurit­y New Zealand is assessing fall armyworm using their emerging risk system due to the recent detection in northern Australia. The system is designed to proactivel­y identify and manage potential and emerging biosecurit­y risks based on significan­t changes to the risk profile (distributi­on, hosts or virulence) of exotic organisms. Biosecurit­y New Zealand is also undertakin­g climate modelling to better understand the potential for establishm­ent, and the impacts and possible distributi­on if fall armyworm were to arrive.


Growers are encouraged to keep an eye out for unusual insects. If you think you have spotted fall armyworm, call the Ministry for Primary Industries (MPI) exotic pest and disease hotline on 0800 80 99 66.

 ??  ?? Photo: Lyle Buss, University of Florida,
Photo: Lyle Buss, University of Florida,
 ??  ?? Photos: Graham Walker, Plant & Food Research.
Photos: Graham Walker, Plant & Food Research.
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